1. Field of the Invention
The present invention relates to motor fuel suitable, for example, in diesel, gas-turbine, and turbojet engines, and especially in standard engines. This motor fuel includes fuel compositions of organic compounds containing bound oxygen, and, optionally, hydrocarbon compounds. In addition, this invention relates to fuel compositions that are stable, homogeneous liquids under normal operating conditions of the engines mentioned above.
2. Background to the Invention
Reduction of pollutants in exhaust emissions of diesel engines represents a challenge to modern society. It has been proposed to replace diesel oil, for example, EN 590 and No. 2 diesel oil, and the like, as a fuel for vehicles, because of environmental reasons and also due to its effects on health. There are international agreements providing for the progressive tightening of the requirements concerning the amount of toxic products resulting from combustion of motor fuel in the exhaust emissions of vehicles and other machines using diesel engines. In the European Union countries and in the United States, the requirements of Step II come into effect in the year 2002. Such requirements mandate a significant decrease in carbon monoxide (CO), mixtures of hydrocarbons and nitrogen oxides (HC+NOx), and particles in the exhaust emissions of diesel engines.
Moreover, modern society is preoccupied with the ameliorating the global imbalance of carbon dioxide in the atmosphere, which is linked to the intensive burning of petroleum products, coal and fossil gas. The damage to the carbon dioxide balance in the atmosphere causes global climate warming and has a negative influence on our planet.
In this regard, the development of motor fuel for engines obtained from renewable plant resources is of real significance.
The growing concern for the protection of the environment and stricter standards in the content of harmful components in exhaust emissions forces the industry to develop urgently various alternative fuels that burn more cleanly than the ones that are in use today.
The existing global inventory of vehicles and machinery with standard diesel, gas-turbine and turbojet engines does not currently the complete elimination of hydrocarbon mixtures obtained from mineral resources, for example crude oil, coal and natural gas, as motor fuel. Diesel oil is such a hydrocarbon mixture.
On the other hand, it is possible to replace a portion of hydrocarbons in motor fuel, such as diesel oil, with other organic compounds that provide cleaner exhaust emissions and do not adversely affect engine performance. Gasolines comprising oxygen-containing compounds are widely used. It is also known, for instance, that replacing 15% of the diesel oil by alcohol in motor fuel results in cleaner exhaust and provides acceptable power without modification of existing diesel engines.
However, the problem of using the most widely available and inexpensive alcohols, methanol and ethanol, as a portion of a motor fuel is that these compounds are immiscible with diesel and gas oil fuels. Potentially, alcohols and other oxygen containing compounds should yield environmentally clean products of combustion. However, the combustion process in engines is an extremely complicated phenomenon, which is affected not only by the composition of the fuel, but also by the physical parameters of the fuel, and, initially by the homogeneity of the liquid.
The feasibility and properties of mixtures of petroleum diesel fraction with ethanol was reported in Technical Feasibility of Diesohol, ASAE Paper 79-1052 in 1979. It was stressed in that article that the main problem related to using such a fuel is its tendency for phase separation. Furthermore, the phase separation is significantly affected by the presence of water in the system. At 0° C., a water content of only 0.05% causes separation of a motor fuel consisting of 99% diesel and 0.95% ethanol.
It is widely known that NOx emissions can be reduced by reducing the combustion temperature. One way to achieve this reduced combustion temperature is to add water to the fuel or to separately inject water in the combustion chamber.
However, by adding water phase separation will occur in most fuel systems, especially at lower temperatures, for example below 0° C. EP-A-0 014 992 (BASF) and U.S. Pat. No. 4,356,001 (Sweeney '001) address the problem of water in the fuel composition by including in the fuel polyethers and/or acetals with or without methanol or ethanol. However, when formulating fuel compositions according to the Sweeney '001 patent, one will find that the improved water tolerances are not sufficient in a wider temperature range. The emissions of carbon monoxide, hydrocarbons and soot from such fuels are significantly higher than acceptable emissions.
It is known that alcohol-containing fuels provide relatively low emissions of carbon, carbon oxide and nitrogen oxide (Johnson R. T., Stoffer J. O., Soc. Automot. Eng. (Spec. Publ.) 1983, S.P. 542, 91-104).
A significant part of the developments in the field of hybrid diesel fuels is dedicated to the creation of microemulsions. Microemulsions are thermally stable colloid dispersions in which the particle diameter is on the order of 20-30 Å. In 1977, Backer proposed employing surfactants to form microemulsions of alcohols and hydrocarbons (GB Patent No. 2,002,400). Later, for the same purposes, other emulsifiers were proposed (GB Patent No. 2,115,002; U.S. Pat. Nos. 4,509,950; 4,451,265; and European Patent No. 475,620).
It is possible to achieve a homogeneous composition of diesel fuel incorporating different alcohols and their mixtures. French Patent No. 2453210, to achieve a homogeneous liquid incorporating hydrocarbons and methanol, proposed to add primary aliphatic saturated alcohols of linear and branched structures having from 8 to 15 carbon atoms or mixtures of such alcohols. The avoidance of the separation of the hybrid fuel incorporating the alcohol mixture is also addressed by the European Patent No. 319060.
A study of the performance characteristics of the hybrid fuels confirms the possibility of their use for the operation of diesel engines (Mathur H. B., Babu M. K. Indian Inst. Techn. Journ. Therm. Eng., 1988, 2(3), p. 63-72. Haschimoto, K., et al., Journ. Jap. Petrol. Inst., 1996, v. 39, N2, p. 166-169).
To achieve a homogeneous fuel blend, WO95/02654 proposes using a formulation containing up to 20% of the total volume of ethanol and/or n-propanol, up to 15% of the total volume of fatty acid and/or organic ester, and the remainder comprised of a hydrocarbon liquid. The patent provides examples of compositions in which oleic acid, as well as different organic esters, are used in addition to diesel, ethanol and propanol.
In WO95/02654, all Examples are said to illustrate fuel compositions having a single phase to demonstrate the effectiveness of using certain amounts of fatty acids and/or organic esters, as well as their mixtures, to obtain homogeneous liquids incorporating diesel and low alkyl alcohols in addition to those mentioned above. However, this patent does not provide any temperature limits with regard to stability of the obtained fuel formulations, and is silent as to how the presence of water in the compositions affects stability.
In addition, WO95/02654 fails to teach or suggest use of at least two oxygen-containing organic compounds containing in total at least four specific functional groups.
It is well known that stability of mixtures of lower alcohols and diesel is one of the main operational properties of such fuels. In WO95/02654, tests of several compositions in various standard diesel engines did not show a decrease of power and efficiency of the fuel. However, nothing is said regarding the content of the exhaust emissions of different engines using the proposed fuel formulations. The only comment in that regard is that the use of the ethanol blend over several months in the engine of a Yale Forklift (model GDP 050 RUAS) Mazda XA was likely to be more acceptable with regard to the condition of the air inside the warehouse where the forklift was operated.
The mentioned drawbacks of the fuel compositions of the prior art are eliminated by providing a fuel composition of the present invention.
Contrary to a large number of fuel compositions of the prior art that have been used to replace diesel fuel in part or in total, especially compositions containing carboxylic acids, the fuel of the present invention is essentially non-corrosive.